Electrolytic capacitor comprising an electrolytic solution containing a first base component, a first acid component, and a second acid component

ABSTRACT

An electrolytic capacitor includes an anode body having a dielectric layer disposed on a surface of the anode body, a solid electrolyte layer that is in contact with the dielectric layer, and an electrolytic solution. The solid electrolyte layer includes a conductive polymer. The electrolytic solution contains a first base component, a first acid component, and a second acid component. The first base component includes an amidine compound. The first acid component includes a composite compound of an inorganic acid and an organic acid. The second acid component includes at least one selected from a group consisting of boric acid, phosphoric acid, phosphorous acid, hypophosphorous acid, and phosphonic acid.

RELATED APPLICATIONS

This application is a continuation of the PCT International ApplicationNo. PCT/JP2019/019822 filed on May 20, 2019, which claims the benefit offoreign priority of Japanese patent application No. 2018-096710 filed onMay 21, 2018, the contents all of which are incorporated herein byreference.

BACKGROUND 1. Technical Field

The present disclosure relates to an electrolytic capacitor including asolid electrolyte layer containing a conductive polymer.

2. Description of the Related Art

As a small-sized, large-capacitance capacitor having a low equivalentseries resistance (ESR), an electrolytic capacitor is seen as promising,the electrolytic capacitor including an anode body having a dielectriclayer formed thereon and a solid electrolyte layer formed to cover atleast a part of the dielectric layer.

Unexamined Japanese Patent Publication No. 2015-165550 discloses that anelectrolytic solution contains an ammonium salt and a composite compoundof an inorganic acid and an organic acid as solutes in order to improvethe withstand voltage of the electrolytic capacitor.

SUMMARY

An electrolytic capacitor according to an aspect of the presentdisclosure includes an anode body having a dielectric layer disposed ona surface of the anode body, a solid electrolyte layer that is incontact with the dielectric layer, and an electrolytic solution. Thesolid electrolyte layer includes a conductive polymer. The electrolyticsolution contains a first base component, a first acid component, and asecond acid component. The first base component includes an amidinecompound. The first acid component includes a composite compound of aninorganic acid and an organic acid. The second acid component includesat least one selected from the group consisting of boric acid,phosphoric acid, phosphorous acid, hypophosphorous acid, and phosphonicacid.

According to the present disclosure, an electrolytic capacitor excellentin reliability can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view illustrating an electrolyticcapacitor according to an exemplary embodiment of the presentdisclosure; and

FIG. 2 is a schematic view for explaining a configuration of a capacitorelement according to the exemplary embodiment.

DETAILED DESCRIPTION OF EMBODIMENT

Unexamined Japanese Patent Publication No. 2015-165550 proposes that asthe solutes of the electrolytic solution, the electrolytic solutioncontains an ammonium salt and a composite compound of an inorganic acidand an organic acid.

However, in the electrolytic capacitor described in Unexamined JapanesePatent Publication No. 2015-165550, there is a possibility that theelectrolytic solution may deteriorate, and a leakage current mayincrease because the recoverability of the dielectric layer of theelectrolytic capacitor cannot be maintained.

Hereinafter, the present disclosure will be described more specificallybased on an exemplary embodiment. However, the following exemplaryembodiment does not limit the present disclosure.

FIG. 1 is a schematic cross-sectional view illustrating an electrolyticcapacitor according to the present exemplary embodiment, and FIG. 2 is aschematic view in which a part of a capacitor element of theelectrolytic capacitor is developed.

The electrolytic capacitor includes, for example, capacitor element 10,bottomed case 11 that houses capacitor element 10, sealing member 12that closes an opening of bottomed case 11, seat plate 13 that coverssealing member 12, lead wires 14A, 14B, lead tabs 15A, 15B, and anelectrolyte (not shown). Lead wires 14A, 14B are drawn out from sealingmember 12 and penetrate seat plate 13. Lead tabs 15A, 15B connect thelead wires and the electrodes of capacitor element 10. And theelectrolyte contains an electrolytic solution and a solid electrolyte.The vicinity of the opening end of bottomed case 11 is drawn inward, andthe opening end is curled to swage sealing member 12.

Capacitor element 10 is formed from a wound body as shown in FIG. 2. Thewound body includes anode body 21 connected to lead tab 15A, cathodebody 22 connected to lead tab 15B, and separator 23. The wound body is asemi-finished product in which the solid electrolyte layer is not formedbetween anode body 21 and cathode body 22.

Anode body 21 and cathode body 22 are wound with separator 23 interposedtherebetween. The outermost circumference of the wound body is fixedwith winding stop tape 24. Note that FIG. 2 shows a state in which apart of the wound body is developed before the outermost circumferenceof the wound body is stopped. As a material of separator 23, forexample, a nonwoven fabric containing, as a main component, cellulose,polyethylene terephthalate, vinylon, aramid fiber, or the like can beused.

Anode body 21 includes a metal foil whose surface is roughened to haveirregularities, and a dielectric layer is formed on the metal foilhaving irregularities. The solid electrolyte layer is formed byattaching a conductive polymer to at least a part of the surface of thedielectric layer. The solid electrolyte layer may cover at least a partof the surface of cathode body 22 and/or the surface of separator 23.Capacitor element 10 in which the solid electrolyte layer is formed ishoused in bottomed case 11 together with the electrolytic solution.

The conductive polymer included in the solid electrolyte layer is aπ-conjugated conductive polymer, and polypyrrole, polythiophene,polyaniline, etc., are preferable. In the present description,polypyrrole, polythiophene, polyaniline, etc., mean polymers having abasic skeleton of polypyrrole, polythiophene, polyaniline, etc.,respectively. Thus, polypyrrole, polythiophene, polyaniline, etc., mayinclude their respective derivatives. Polythiophene includes, forexample, poly(3,4-ethylenedioxythiophene) (PEDOT), etc., that arederivatives of polythiophene. These may be used alone, two or more typesmay be used in combination, or a copolymer of two or more types ofmonomers may be used. The weight average molecular weight of theconductive polymer is not particularly limited, but is, for example,ranges from 1000 to 100,000, inclusive. The solid electrolyte layer mayfurther include a dopant.

The electrolytic solution of the present exemplary embodiment contains asolvent, a first base component, a first acid component, and a secondacid component.

It is preferable that the solvent includes a glycol compound. Examplesof the glycol compound include, for example, alkylene glycol andpolyalkylene glycol having a weight average molecular weight less thanor equal to 300. More specifically, examples of the glycol compoundinclude ethylene glycol, propylene glycol, butylene glycol, pentyleneglycol, hexylene glycol, diethylene glycol, triethylene glycol,tetraethylene glycol, pentaethylene glycol, hexaethylene glycol, etc.These may be used alone or in combination of two or more types. Inparticular, ethylene glycol, propylene glycol, butylene glycol(butanediol), pentylene glycol (pentanediol), etc., have a low viscosityeven among glycol compounds having a weight average molecular weightless than or equal to 300, so that a solute is easily dissolved, thermalconductivity is high, and the heat dissipation when a ripple current isgenerated is excellent. Hence, heat resistance can be improved. Inparticular, ethylene glycol has a large effect of improving heatresistance.

The solvent may further contain a sulfone compound. The sulfone compoundis an organic compound having in its molecule a sulfonyl group (—SO₂—).Examples of the sulfone compound include, for example, chain sulfone andcyclic sulfone. Examples of the chain sulfone include, for example,dimethyl sulfone, diethyl sulfone, dipropyl sulfone, and diphenylsulfone. Examples of the cyclic sulfone include, for example, sulfolane,3-methylsulfolane, 3,4-dimethylsulfolane, and3,4-diphenylmethylsulfolane. In particular, it is preferable that thesulfone compound is sulfolane from the viewpoints of dissociation ofsolute and thermal stability. Since sulfolane has a low viscosity amongsulfone compounds, it easily dissolves a solute.

Examples of other components of the solvent include, for example, alactone compound and a carbonate compound. Examples of the lactonecompound include, for example, γ-butyrolactone (GBL) andγ-valerolactone. Examples of the carbonate compound include, forexample, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), andfluoroethylene carbonate (FEC). These may be used alone or incombination of two or more types. In particular, the other component ispreferably a lactone compound, and more preferably GBL, from theviewpoint of thermal stability.

The first base component includes an amidine compound. The amidinecompound is a compound having an alkyl-substituted amidine group, andexamples thereof include, for example, a cyclic amidine compound or aquaternary compound thereof (amidinium compound). Specific examplesthereof include an imidazoline compound, imidazole compound,benzimidazole compound, alicyclic pyrimidine compound, etc., which arequaternized with an alkyl group or an arylalkyl group each having 1 to11 carbon atoms. More specifically, examples thereof include1-methyl-1,8-diazabicyclo[5,4,0]undecene-7,1-methyl-1,5-diazabicyclo[4,3,0]nonene-5,1,2,3-trimethylimidazolinium,1,2,3,4-tetramethylimidazolinium, 1,3-dimethyl-2-ethyl-imidazolinium,1,3,4-trimethyl-2-ethylimidazolinium,1,3-dimethyl-2-heptylimidazolinium,1,3-dimethyl-2-(-3′heptyl)imidazolinium,1,3-dimethyl-2-dodecylimidazolinium,1,2,3-trimethyl-1,4,5,6-tetrahydropyrimidium, 1,3-dimethylimidazolium,1,3-dimethylbenzimidazolium, etc.

The first acid component contains a composite compound of an organicacid and an inorganic acid. As the composite compound of an organic acidand an inorganic acid, borodisalicylic acid, borodioxalic acid,borodiglycolic acid, etc., which have high heat resistance, arepreferable.

The second acid component includes at least one selected from the groupconsisting of boric acid, phosphoric acid, phosphorous acid,hypophosphorous acid, and phosphonic acid. The second acid component maybe esterified. For example, an example of the esterified product of thesecond acid component includes a condensate obtained by condensing apart of the hydroxyl groups of the second acid component with an alcoholcompound, a glycol compound, or the like.

The electrolytic solution containing the composite compound of anorganic acid and an inorganic acid as the first acid component is likelyto have a high acidity. Meanwhile, in the present exemplary embodiment,a pH of the electrolytic solution does not become too low because theelectrolytic solution contains an amidine compound, which has a higherbasicity than an amine compound such as a primary amine compound, asecondary amine compound, or a tertiary amine compound, as the firstbase component. Thus, corrosion of the anode body can be suppressed, andthe reliability of the electrolytic capacitor can be enhanced.

Further, by containing the second acid component in the electrolyticsolution, decomposition of the first acid component can be suppressed.Thus, in the electrolytic capacitor in which the solid electrolyte layerincluding the conductive polymer is in contact with the dielectriclayer, deterioration of the electrolytic solution can be suppressed.Hence, recoverability of the dielectric layer is maintained even whenused for a long time, thereby suppressing an increase in a leakagecurrent. From the viewpoint of suppressing decomposition of the firstacid component, it is preferable that the second acid component is boricacid. The second acid component may be esterified in the electrolyticsolution.

In the electrolytic solution, a content proportion of a total amount ofthe first base component and the first acid component preferably rangesfrom 5 wt % to 35 wt %, inclusive, and more preferably from 5 wt % to 30wt %, inclusive. By setting it to be within this range, sufficientelectric conductivity of the electrolytic solution can be obtained andthe recoverability of the dielectric layer can be enhanced, in theelectrolytic capacitor in which the solid electrolyte layer includingthe conductive polymer is in contact with the dielectric layer.

In the electrolytic solution, a content proportion of an amount of thesecond acid component preferably ranges from 0.1 wt % to 15 wt %,inclusive. By setting it to be more than or equal to 0.1 wt %,decomposition of the first acid component can be further suppressed. Bysetting it to be less than or equal to 15 wt %, precipitation of thesecond acid component in the electrolytic solution can be suppressed.

The electrolytic solution may further contain a second base component.Examples of the secondary base component include a primary aminecompound, secondary amine compound, tertiary amine compound, andquaternary ammonium compound. Examples of the primary amine includemethylamine, ethylamine, propylamine, etc., examples of the secondaryamine include dimethylamine, diethylamine, ethylmethylamine,dibutylamine, etc., and examples of the tertiary amine includetrimethylamine, triethylamine, tributylamine, ethyldiisopropylamine,etc. Examples of the quaternary ammonium ion of a quaternary ammoniumsalt include tetramethylammonium, triethylmethylammonium,tetraethylammonium, etc. By containing the second base component in theelectrolytic solution, the electrolytic solution can be suppressed frombecoming too low in pH.

It is preferable that the second base component is weakly alkaline(e.g., pH is less than or equal to 11 in aqueous solution).

The secondary base component may be a primary to tertiary amine compoundhaving a hydroxyl group. Examples of the primary to tertiary aminecompound having a hydroxyl group include an aliphatic primary totertiary amine compound, etc., and in particular an aliphatic primaryamine compound is more preferable. Examples of the aliphatic primaryamine compound having a hydroxyl group include monomethanolamine,monoethanolamine, dihydroxymethylaminomethane,trishydroxymethylaminomethane, etc., which are weakly alkaline. From theviewpoint of suppressing corrosion of the anode body, an aliphaticprimary amine compound having two or more hydroxyl groups is preferable,and an aliphatic primary amine compound having three or more hydroxylgroups is further preferable. As the aliphatic primary amine compoundhaving three or more hydroxyl groups, trishydroxymethylaminomethane ispreferable.

It is preferable that the pH of the electrolytic solution in the presentexemplary embodiment ranges from 1.5 to 5.5, inclusive. By setting thepH to be less than or equal to 5.5, dedoping of a dopant from theconductive polymer is suppressed when the conductive polymer containsthe dopant, so that an increase in ESR due to the dedoping of the dopantcan be suppressed. Also, by setting the pH to be more than or equal to1.5, corrosion of the anode body can be suppressed.

The pH of the electrolytic solution can be adjusted by adding the secondbasic component. It is preferable that the pH of the electrolyticsolution to which the second basic component has been added ranges from1.5 to 5.5, inclusive. By containing the second base component in theelectrolytic solution, the electrolytic solution can be suppressed frombecoming too low in pH. Further, when the aliphatic primary aminecompound is used as the second base component, the electrolytic solutioncan be suppressed from becoming too high in pH.

The electrolytic solution may include a third acid component. It ispreferable that the third acid component is a nitro compound. Examplesof the nitro compound include a compound having a nitro group and acarboxyl group, a compound having a nitro group and a hydroxyl group, acompound having a nitro group and a hydroxyalkyl group, etc. Examples ofthe compound having a nitro group and a carboxyl group include, forexample, o-nitrobenzoic acid, m-nitrobenzoic acid, p-nitrobenzoic acid,nitrobenzene dicarboxylic acid, dinitrobenzenecarboxylic acid,nitrotoluenecarboxylic acid, nitroanisolecarboxylic acid, etc. Examplesof the compound having a nitro group and a hydroxyl group includeo-nitrophenol, m-nitrophenol, p-nitrophenol, p-nitroacetophenone, etc.Examples of the compound having a nitro group and a hydroxyalkyl groupinclude o-nitrobenzyl alcohol, m-nitrobenzyl alcohol, p-nitrobenzylalcohol, nitrobenzeneethanol, etc. By containing the third acidcomponent in the electrolytic solution, decomposition of the first acidcomponent can be further suppressed. It is preferable that a contentproportion of an amount of the third acid component in the electrolyticsolution ranges from 0.1 wt % to 15 wt %, inclusive. By setting it to bemore than or equal to 0.1 wt %, decomposition of the first acidcomponent can be further suppressed. By setting it to be less than orequal to 15 wt %, precipitation of the third acid component can besuppressed in the electrolytic solution. In particular, o-nitrobenzoicacid, m-nitrobenzoic acid, and p-nitrobenzoic acid are preferable as thethird acid component, from the viewpoint of suppressing decomposition ofthe first acid component.

In the electrolytic capacitor of the present exemplary embodiment, thefirst acid component and the second acid component are contained. Hence,decomposition of the first acid component can be further suppressed, andthe electrolytic solution is prevented from becoming too low in pH bythe first basic component, even when self-heating occurs due to, forexample, a ripple current while in use. Hence, deterioration of theelectrolytic solution due to heat can be suppressed in the electrolyticcapacitor of the present exemplary embodiment, and thus therecoverability of the dielectric layer can be maintained and an increasein a leakage current can be suppressed.

Hereinafter, an example of the method of producing the electrolyticcapacitor according to the present exemplary embodiment will bedescribed for each step.

(i) Step of Preparing Anode Body 21 Having Dielectric Layer

First, a metal foil that is a raw material of anode body 21 is prepared.The type of the metal is not particularly limited, but it is preferableto use a valve metal such as aluminum, tantalum, or niobium or an alloycontaining the valve metal, from the viewpoint of easy formation of thedielectric layer.

Next, a surface of the metal foil is roughened. By the roughening, aplurality of irregularities are formed on the surface of the metal foil.It is preferable that the roughening is performed by etching the metalfoil. The etching may be performed by, for example, a direct currentelectrolysis method or an alternating current electrolysis method.

Next, the dielectric layer is formed on the roughened surface of themetal foil. The forming method is not particularly limited, but thedielectric layer can be formed by subjecting the metal foil to ananodizing treatment. In the anodizing treatment, for example, the metalfoil is immersed in an anodizing liquid such as an ammonium adipatesolution, and is subjected to a heat treatment. Alternatively, the metalfoil may be immersed in the anodizing liquid and a voltage may beapplied.

From the viewpoint of mass productivity, a roughening treatment and theanodizing treatment are usually performed on a large-sized foil (metalfoil) made of the valve metal or the like. In that case, anode body 21is prepared by cutting the treated foil into a desired size.

(ii) Step of Preparing Cathode Body 22

A metal foil can be used for cathode body 22 similarly to the anodebody. The type of the metal is not particularly limited, but it ispreferable to use a valve metal such as aluminum, tantalum, or niobiumor an alloy containing the valve metal. If necessary, a surface ofcathode body 22 may be roughened. In addition, an oxide film anodized atabout 2 V or a metal film made of titanium, nickel, or the like and/or acarbon film may be formed on the surface of cathode body 22.

(iii) Step of Forming Wound Body

Next, a wound body is formed by using anode body 21 and cathode body 22.

First, anode body 21 and cathode body 22 are wound while interposingseparator 23 between them. At this time, lead tabs 15A, 15B can beerected from the wound body as shown in FIG. 2 by winding while rollingup lead tabs 15A, 15B.

As the material of separator 23, a non-woven fabric including, forexample, natural cellulose, synthetic cellulose, polyethyleneterephthalate, vinylon, aramid fiber, or the like as a main componentcan be used.

The material of lead tabs 15A, 15B is not particularly limited as longas it is a conductive material. The material of lead wires 14A, 14B,which are to be respectively connected to lead tabs 15A, 15B, are alsonot particularly limited as long as those are conductive material.

Next, fixing tape 24 is disposed on the outer surface of cathode body 22located in the outermost layer of a wound body in which anode body 21,cathode body 22, and separator 23 are wound, and an end of cathode body22 is fixed with fixing tape 24. When anode body 21 is formed by cuttingthe large-sized metal foil, the wound body may be further subjected tothe anodizing treatment in order to form the dielectric layer on acutting surface of anode body 21.

(iv) Step of Forming Capacitor Element 10

Next, a film including a conductive polymer which covers at least a partof the dielectric layer is formed by, for example, impregnating thedielectric layer with a polymer dispersion or a polymer solution. Thepolymer dispersion contains a liquid component and the conductivepolymer dispersed in the liquid component. The polymer solution is asolution in which the conductive polymer is dissolved in a liquidcomponent. Next, a dense solid electrolyte layer covering at least apart of the dielectric layer is formed by volatilizing the liquidcomponent from the formed film by drying. Since the conductive polymeris uniformly distributed in the liquid component of the polymerdispersion, a uniform solid electrolyte layer can be easily formed bythe polymer dispersion. In this way, capacitor element 10 can beobtained.

The polymer dispersion can be obtained by, for example, a method ofdispersing a conductive polymer in a liquid component, a method ofpolymerizing a precursor monomer in a liquid component to generate theparticles of a conductive polymer, or the like. An example of thepreferred polymer dispersion includes, for example,poly(3,4-ethylenedioxythiophene) (PEDOT) doped with polystyrene sulfonicacid (PSS), that is, PEDOT/PSS.

The liquid component may be water, a mixture of water and a non-aqueoussolvent, or a non-aqueous solvent. The non-aqueous solvent is notparticularly limited, but for example, a protic solvent or an aproticsolvent can be used. Examples of the protic solvent include: alcoholssuch as methanol, ethanol, propanol, butanol, ethylene glycol, andpropylene glycol; ethers such as formaldehyde and 1,4-dioxane; and thelike. Examples of the aprotic solvent include: amides such asN-methylacetamide, N,N-dimethylformamide, and N-methyl-2-pyrrolidone;esters such as methyl acetate; ketones such as methyl ethyl ketone; andthe like.

The step of providing the polymer dispersion to the surface of thedielectric layer and the step of drying the wound body may be repeatedtwice or more. By performing these steps multiple times, the coverage ofthe dielectric layer by the solid electrolyte layer can be increased. Atthis time, the solid electrolyte layer may be formed not only on thesurface of the dielectric layer but also on the surfaces of cathode body22 and separator 23.

From the above, the solid electrolyte layer is formed between anode body21 and cathode body 22, so that capacitor element 10 is formed. Thesolid electrolyte layer formed on the surface of the dielectric layersubstantially functions as a cathode material.

(v) Step of Preparing Electrolytic Solution and Impregnating CapacitorElement 10 with Electrolytic Solution

Next, the above-described solute (acid component and base component) isdissolved in a solvent to prepare the electrolytic solution, and thencapacitor element 10 is impregnated with the electrolytic solution. Themethod of impregnating capacitor element 10 with the electrolyticsolution is not particularly limited. For example, a method of immersingcapacitor element 10 in the electrolytic solution housed in a containeris simple and preferable. The immersion time also depends on the size ofcapacitor element 10, but ranges, for example, from 1 second to 5minutes. It is preferable that the impregnation is performed underreduced pressure, for example, in an atmosphere ranging from 10 kPa to100 kPa, and preferably from 40 kPa to 100 kPa.

(vi) Step of Sealing Capacitor Element

Next, capacitor element 10 is sealed. Specifically, capacitor element 10is first housed in bottomed case 11 such that lead wires 14A, 14B arelocated at a side of the open upper surface of bottomed case 11. As thematerial of bottomed case 11, a metal such as aluminum, stainless steel,copper, iron, or brass, or an alloy thereof can be used.

Next, sealing member 12 configured such that lead wires 14A, 14Bpenetrate sealing member 12 is disposed above capacitor element 10, sothat capacitor element 10 is sealed in bottomed case 11. Next, thevicinity of the open end of bottomed case 11 is subjected to a lateraldrawing, and the open end is curled to swage sealing member 12. Then, bydisposing seat plate 13 on the curled portion, the electrolyticcapacitor as shown in FIG. 1 is completed. Then, an aging treatment maybe performed while the rated voltage is being applied.

Although the winding-type electrolytic capacitor has been described inthe above exemplary embodiment, the scope of application of the presentdisclosure is not limited to the above. The present disclosure can beapplied to other electrolytic capacitors including, for example, achip-type electrolytic capacitor using a sintered metal body as an anodebody and a laminated-type electrolytic capacitor using a metal plate asan anode body.

EXAMPLES

The present disclosure will be described in more detail based onexamples, but the present disclosure is not limited to the examples.

In the following examples, a winding-type electrolytic capacitor (φ(diameter) 10 mm×L (length) 10 mm) having a rated voltage of 25 V and arated electrostatic capacity of 330 μF was produced. A specific methodof producing the electrolytic capacitor will be described below.

(Preparation of Anode Body)

An aluminum foil having a thickness of 100 μm was subjected to anetching treatment to roughen the surface of the aluminum foil. Then, adielectric layer was formed on the surface of the aluminum foil by ananodizing treatment. The anodizing treatment was performed by immersingthe aluminum foil in an ammonium adipate solution and applying a voltageof 50 V to the aluminum foil. Then, the aluminum foil was cut to preparean anode body.

(Preparation of Cathode Body)

An aluminum foil having a thickness of 50 μm was subjected to an etchingtreatment to roughen the surface of the aluminum foil. Then, thealuminum foil was cut to prepare a cathode body.

(Production of Wound Body)

An anode lead tab and a cathode lead tab were connected to the anodebody and the cathode body, respectively, and the anode body and thecathode body were wound interposing a cellulose separator while the leadtabs were being rolled up. An anode lead wire and a cathode lead wirewere connected to the ends of the lead tabs protruding from the woundbody, respectively. The formed wound body was subjected to an anodizingtreatment again to form a dielectric layer on the cutting end of theanode body. Next, the end of the outer surface of the wound body wasfixed with a fixing tape to produce a wound body.

(Preparation of Polymer Dispersion)

A mixed solution was prepared by dissolving, in ion-exchanged water,3,4-ethylenedioxythiophene and polystyrene sulfonic acid (PSS, weightaverage molecular weight 100,000) that is a polymer dopant. While themixed solution was stirred, iron(III) sulfate (oxidant) dissolved inion-exchanged water was added to perform a polymerization reaction.After the reaction, the obtained reaction solution was dialyzed toremove the unreacted monomer and excess oxidant, so that a polymerdispersion containing polyethylenedioxythiophene doped with about 5% bymass of PSS (PEDOT/PSS) was obtained.

(Formation of Solid Electrolyte Layer)

The wound body was immersed in the polymer dispersion housed in acontainer for 5 minutes in a reduced pressure atmosphere (40 kPa), andthen the wound body was pulled out from the polymer dispersion. Next,the wound body impregnated with the polymer dispersion was dried in adrying oven at 150° C. for 20 minutes to form a solid electrolyte layerconstituted by a conductive polymer layer covering at least a part ofthe dielectric layer.

(Impregnation With Electrolytic Solution)

An electrolytic solution containing a first acid component, a first basecomponent, a second acid component, a second base component, and varioussolvents, which are in the composition shown in Table 1, was prepared,and the wound body was immersed in the electrolytic solution for 5minutes in a reduced pressure atmosphere (40 kPa). The numerical valuesin Table 1 indicate the content proportions (unit: wt %) of therespective components in the electrolytic solution.

TABLE 1 First base component/ First acid Solvent Second acid Third acidSecond base component PEG component component component TMI/BSA GBL EGSL 300 BA PA PNA THAM Example 1 5 55 — 12 25 3 — — — Example 2 10 50 —12 25 3 — — — Example 3 15 45 — 12 25 3 — — — Example 4 30 30 — 12 25 3— — — Example 5 15 — 45 12 25 3 — — — Example 6 15 45 — 12 25 — 3 — —Example 7 15 44 — 12 25 3 1 — — Example 8 15 45 — 12 25 3 — — 1 Example9 15 45 — 12 25 3 — 1 — Comparative 15 48 — 12 25 — — — — Example 1Comparative 25 — 30 20 25 — — — — Example 2 TMI/BSA:1,2,3,4-Tetramethylimidazolinium/Borodisalicylic acid GBL:γ-Butyrolactone EG: Ethylene glycol SL: Sulfolane PEG 300: Polyethyleneglycol having weight average molecular weight of 300 BA: Boric acid PA:Phosphoric acid PNA: p-Nitrobenzoic acid THAM:Trishydroxymethylaminomethane(Sealing of Capacitor Element)

A capacitor element impregnated with the electrolytic solution wassealed to complete the electrolytic capacitors as shown in FIG. 1(Examples 1 to 9 and Comparative examples 1 and 2). Then, an agingtreatment was performed at 130° C. for 2 hours, while the rated voltagewas being applied.

[Evaluation]

Initial leakage current X0 (LC) and initial equivalent series resistanceY0 (ESR) of the obtained electrolytic capacitor were measured.

Next, in order to evaluate long-term reliability, a rate of change inleakage current (ΔLC) and a rate of change in ESR (ΔESR) were evaluatedby holding the electrolytic capacitor at 145° C. for 4,000 hours whilethe rated voltage was being applied.

ΔLC was shown by the ratio (X/X0) of LC (X) that is a value after theholding at 145° C. to the initial value (X0). As the leakage current, aleakage current was measured in a condition in which a voltage of 25 Vwas applied between the anode body and the cathode body of theelectrolytic capacitor for 120 seconds at room temperature.

ΔESR was shown by the ratio (Y/Y0) of ESR (Y) that is a value after theholding at 145° C. to the initial value (Y0). ESR of the electrolyticcapacitor was measured using an LCR meter at a frequency of 100 kHz atroom temperature.

Table 2 shows evaluation results.

TABLE 2 Leakage current Equivalent series resistance (LC) measurement(ESR) measurement After After Initial load ΔLC Initial load ΔESR Xo[μA]X[μA] X/Xo Yo[mΩ] Y[mΩ] Y/Y Example 1 4.2 4.3 1.02 11.0 16.3 1.48Example 2 4.1 4.2 1.02 11.4 17.1 1.50 Example 3 3.8 3.7 0.97 11.8 18.91.60 Example 4 3.5 3.2 0.91 12.1 23.0 1.90 Example 5 3.9 3.8 0.97 10.815.1 1.40 Example 6 3.4 3.9 1.15 11.0 15.4 1.40 Example 7 3.8 3.9 1.0310.8 14.0 1.30 Example 8 3.2 2.3 0.72 12.1 20.6 1.70 Example 9 3.4 3.20.94 10.5 13.7 1.30 Comparative 3.8 11.5 3.03 12.5 31.3 2.50 Example 1Comparative 3.9 12.9 3.31 11.3 24.9 2.20 Example 2

In each of Examples 1 to 9, the reliability of the electrolyticcapacitor was able to be enhanced as compared with that in each ofComparative examples 1 and 2.

The present disclosure can be used in an electrolytic capacitorincluding both a solid electrolyte layer covering at least a part of adielectric layer and an electrolytic solution.

What is claimed is:
 1. An electrolytic capacitor comprising: an anodebody having a dielectric layer disposed on a surface of the anode body;a solid electrolyte layer that is in contact with the dielectric layer,the solid electrolyte layer including a conductive polymer; and anelectrolytic solution, wherein: the electrolytic solution contains afirst base component, a first acid component, and a second acidcomponent, the first base component includes an amidine compound, thefirst acid component includes a composite compound of an inorganic acidand an organic acid, the second acid component includes at least oneselected from a group consisting of boric acid, phosphoric acid,phosphorous acid, hypophosphorous acid, and phosphonic acid, and acontent proportion of the second acid component in the electrolyticsolution ranges from 3 wt % to 15 wt %, inclusive.
 2. The electrolyticcapacitor according to claim 1, wherein the first acid componentincludes at least one selected from a group consisting ofborodisalicylic acid, borodiglycolic acid, and borodioxalic acid.
 3. Theelectrolytic capacitor according to claim 1, wherein: the electrolyticsolution further contains a second base component, and the second basecomponent includes at least one selected from a group consisting of aprimary amine compound, a secondary amine compound, a tertiary aminecompound, and a quaternary ammonium compound.
 4. The electrolyticcapacitor according to claim 3, wherein: the second base component isthe primary amine compound, and the primary amine compound is analiphatic primary amine compound having a hydroxyl group.
 5. Theelectrolytic capacitor according to claim 4, wherein the aliphaticprimary amine compound having a hydroxyl group has three or morehydroxyl groups.
 6. The electrolytic capacitor according to claim 1,wherein: the electrolytic solution contains a solvent, and the solventincludes a glycol compound.
 7. The electrolytic capacitor according toclaim 6, wherein a weight average molecular weight of the glycolcompound is less than or equal to
 300. 8. The electrolytic capacitoraccording to claim 1, wherein a content proportion of a total amount ofthe first base component and the first acid component in theelectrolytic solution ranges from 5 wt % to 30 wt %, inclusive.
 9. Theelectrolytic capacitor according to claim 1, wherein the second acidcomponent is boric acid.
 10. The electrolytic capacitor according toclaim 1, wherein a pH of the electrolytic solution ranges from 1.5 to5.5, inclusive.
 11. The electrolytic capacitor according to claim 1,wherein: the electrolytic solution further contains a third acidcomponent, and the third acid component includes a nitro compound.